Which Features Do You Need in a Power Bank?

Watching your phone or tablet steadily run out of juice when you're nowhere near a power outlet is stressful. Fortunately, there's no shortage of third-party backup batteries. And they come in every size and capacity (and price range) to keep your device going when your battery icon starts to dip in the red. And it doesn't end there. Some power banks are equipped with features like fast charging, wireless charging, built-in cables, AC adapters, LED flashlights—even the ability to jump-start your car.

With so many options to choose from, how do you know which power bank is right for you? Read on for the most important points to consider, as well as the best battery packs we've tested.

Size and Capacity

Generally speaking, the bigger the battery, the higher the capacity and quantity of ports you get. Power banks that fit comfortably in your pocket are typically good for a full phone charge or two, while anything designed to keep you going all day is going to require a bag or a purse.

On the pocket-friendly front, most smaller batteries that maximize portability have a capacity of 3,500mAh and under, which gives you just enough charge to top up most phones once.

Once you get above 3,500mAh, battery size increases to the point where it's less likely to fit into your skinny jeans, but can still be stowed in a jacket pocket. The Anker PowerCore 10000, for instance, packs a generous 10,000mAh (good for about three full phone charges) in a 7.0-ounce slab you can carry with little difficulty.

If you're planning on being off the grid for an extended period, you're looking at a battery with a capacity of 15,000mAh or higher. Some, like the Mophie PowerStation AC and iMuto Portable Charger X6 Pro, come with high-output AC and USB-C ports (respectively) to let you power laptops, and have enough juice to charge the average phone 10 times. Of course, they're some of the biggest and heaviest of the bunch, and definitely need to be carried in a bag.

Input and Output Ports

The type of port (or ports) a battery has determines not only whether it is compatible with the devices you want to charge, but also charging speed. At a minimum, most battery packs will have a standard micro USB port for input and a USB-A port for output. But with more phones, tablets, and laptops adopting the USB-C standard, you'll often find a USB-C port in addition to USB-A.

USB-C generally allows you to charge faster, consolidates input/output to one port, and can be found in many new phones. Now, you do have to be careful, because while some power banks have USB-C input, they don't have USB-C output. On the Mi Power Bank Pro, for instance, plugging a USB-C device in results in that device trying to charge the battery rather than vice versa. Make sure that both the port and cable you use are up to spec.

Lightning is a proprietary Apple technology, so companies need to pay Apple when they use it; that makes it a bit less common to find. We've reviewed a few Lightning batteries, like the Aukey Portable Charger, but they didn't quite make the cut for this list.

Fast Charging

Another factor to consider is how fast a power bank can charge your phone. Battery output is measured in voltage and amperage. Amperage (or current) is the amount of electricity flowing from the battery to the connected device, while voltage is the amount of potential energy. Multiplying volts by amps gives you wattage, the measure of total power. In order to make a device charge faster, most manufacturers either vary the voltage or boost the amperage in order to increase the total wattage. For most fast charging, you're looking at boosting or dynamically varying the voltage.

Essentially, for any kind of fast charging you need three things: A phone or other device with a charging circuit capable of using one of the fast charging standards, along with a battery and cable that support the same standard. If any one of these three things is missing, you won't be charging as fast as you can.

The two main fast charging standards you're likely to encounter are Samsung's Adaptive Fast Charging and Qualcomm's Quick Charge 3.0. Both work in a similar manner, by increasing voltage rather than amperage. As you might imagine, Samsung's Fast Charging only works with certain Samsung devices, while Qualcomm Quick Charge 3.0 requires that your device has a compatible Snapdragon chipset. These standards allow you to charge supported phones to 50 percent capacity in 30 minutes, which is especially great when you need power in a pinch.

Keep in mind, your phone will only take in as much power as its charging circuit is designed for, so even if you have it plugged into a 5V/2A battery, if it's only able to handle 5V/1A, that's the rate it will charge at.

Pass-Through and Wireless Charging

There are a couple of other aspects to consider before selecting a backup battery. Pass-through charging lets you charge devices connected to the battery, while the battery itself is also being charged. If both your phone and backup battery are running on empty, this is a very useful feature.

Wireless charging is finally in the spotlight, thanks to Apple's use of the technology in its latest iPhones. Qi is the dominant standard that you'll find in compatible Apple and Samsung phones, and there are some battery packs out there that support it. The Mophie Charge Force Powerstation, for instance, uses wireless charging so you can just place your phone on it. And the Belkin Valet Charger has a spot on top where you can stick your Apple Watch.

Should You Buy a Battery Case Instead?

If you find that you often forget to carry your backup battery when you need it most, you might want to think about using a dedicated battery case instead. It combines the portability and protection of a case with a built-in power cell to keep your phone topped off at all times. The downside is that they often have lower charging capacities than dedicated batteries, and you really can't charge anything else with them.

Before buying a power bank, make sure to decide which features are most important to you. To help make things easier, we've included all of our top-rated batteries in the chart above, so you know what you're getting at a glance.

Bottom Line: The iMuto Portable Charger X6 Pro boasts a massive 30,000mAh capacity for a reasonable price, along with numerous ports and fast charging support for charging all of your mobile devices on the go.

About the Author

Ajay Kumar is PCMag's Analyst obsessed with all things mobile. Ajay reviews phones, tablets, accessories, and just about any other gadget that can be carried around with you. In his spare time he games on the rig he built himself, collects Nintendo amiibos, and tries his hand at publishing a novel. Follow Ajay on Twitter @Ajay_H_Kumar. See Full Bio